In LTE (Long Term Evolution) standardized by 3GPP (3rd Generation Partnership Project) which is a standardized organization for radio communication systems, a technique called SON (Self Organizing Network) is employed. According to SON, it is expected that for installation and maintenance of a radio base station, measurement and setting in the field can be automated without needing human intervention (see, for example, Non-patent Literature 1).
In SON, the following method for coverage adjustment is proposed. Specifically, to balance the load between radio base stations (called eNBs in 3GPP), coverage adjustment is made based on load information exchanged between the radio base stations. Such an optimization technique is called MLB (Mobility Load Balancing).
To be more specific, the following pieces of load information are defined in the LTE system: (a) PRB (Physical Resource Blocks) usage (PRB is a unit of time-frequency resource allocation), (b) load on a backhaul between a radio base station and a core network, (c) hardware load on the radio base station, and (d) a capacity class, which is an indicator of the relative communication capacity of the radio base station, and a percentage of communication capacity available in the communication capacity.